If you’re not friends with Steven Chu on Facebook, you missed the Energy Secretary’s post yesterday about a white-topped UPS truck spotted in the nation’s capital. “An encouraging sight drove past my office last week—a UPS delivery truck sporting a white roof,” Chu wrote. “If UPS can set aside its trademark brown color scheme for the sake of a cooler cargo area, hopefully more businesses and consumers will begin to ask themselves: ‘What can white roofs do for you?’”

The answer to that question, as we’ve reported, is that a white (or "cool" as we call 'em) roof could potentially lower the surface temperature of your roof by up to 100°F. That's according to the California Energy Commission, which estimates that cool roofs can trim cooling costs by 20 percent on average in the Golden State.

Cool roofs work by reflecting sunlight. Painting the roof white is one approach. Installing light-toned asphalt shingles or clay tiles with a reflective coating can also redirect the sun’s energy. But cool roofs aren’t for everyone. Homeowners in hot, sunny climate where air conditioning is used a lot will reap the biggest benefits. In other regions, a cool roof could end up increasing heating costs in the winter, so you should use the DOE’s cool-roof calculator to see how much energy you’ll save.

If your home is a candidate for a cool roof and you have asphalt shingles, check the latest Consumer Reports review of roofing materials. The best shingles in our Ratings could last up to 30 years, which is very cool indeed.